The present invention relates to an image reader that can simultaneously read the images on both sides of a document. The invention also relates to an image forming apparatus fitted with such an image reader.
An image reader that can automatically read the images on both sides of a document passing along a document path includes a single reading unit fitted on the path. After the reading unit reads the image on one side of the document, the document is switched back and conveyed back along a portion of the document path so that the reading unit can read the image on the other side.
JP-2002-354201-A discloses an image reader including two reading units fitted on both sides of a document path. Each of the reading units reads the image on one side of a document passing along the document path. This reader can read the images on both sides of a document at a high speed, without the necessity of switching back the document.
When the reading units read the images on both sides of a card or another thick document, however, there is a possibility that the image on one side will be out of focus.
In general, when an image reader reads the image on a thick document passing along a document path, the reader shifts its guide member away from the path, widening the gap between its reading unit and the guide member in accordance with the thickness of the document. If this technique were applied to an image reader for simultaneously reading both sides of a document being conveyed, focal length stabilization might not be effected on one side of the document. This would create a strong possibility that this side of the document might be out of focus.
An object of the present invention is to provide an image reader that can simultaneously read the images on both sides of a document of any thickness, with the images in focus, while the document is conveyed. Another object of the invention is to provide an image forming apparatus fitted with such an image reader.